Pesticides damage survival of bee colonies, landmark study shows

The worlds largest ever field trial demonstrates widely used insecticides harm both honeybees and wild bees, increasing calls for a ban

Widely used insecticides damage the survival of honeybee colonies, the worlds largest ever field trial has shown for the first time, as well as harming wild bees.

The farm-based research, along with a second new study, also suggests widespread contamination of entire landscapes and a toxic cocktail effect from multiple pesticides.

The landmark work provides the most important evidence yet for regulators around the world considering action against neonicotinoids, including in the EU where a total ban is poised to be implemented this autumn. The insecticides are currently banned on flowering crops in the EU.

Neonicotinoids represent a quarter of the multi-billion dollar pesticide market but have been repeatedly linked to serious harm in bees in lab-based studies. Bees and other pollinators are vital to food production but are in decline, in part due to loss of habitats and disease. But there had been few realistic field studies to date to address the role of the insecticides and only occasional evidence for colony-level harm in wild bees.

The new research took place at 33 large farmland sites spread across the UK, Germany and Hungary. Honeybees, bumblebees and solitary bees living by insecticide-treated fields of oil seed rape were compared with those in fields where insecticides were not used in the year of the study.

The survival of honeybee colonies was reduced by exposure to the insecticides in the UK and Hungary, but not in Germany, where the bees foraged far less on oil seed rape and had lower levels of disease. The reproductive success of the wild bees was cut as the insecticide exposure increased in all three countries.

We showed significant negative effects at critical life cycle stages, said Prof Richard Pywell, from the UKs Centre for Ecology and Hydrology (CEH), and part of the research team. If the bees are foraging a lot on oil seed rape, they are clearly at risk. This is a large and important piece of evidence, but it is not the only evidence regulators will look at.

The second new study published in Science, carried out on corn farms in Canada, also found crops were not the main source of neonicotinoids to which bees were exposed. Instead, the contaminated pollen came from wildflowers, as has been shown recently in the UK.

This indicates that neonicotinoids, which are water soluble, spill over from fields into the surrounding environment, where they are taken up by other plants that are very attractive to bees, said Nadia Tsvetkov, at York University in Canada and who led the research.

The detection of the potential long-term persistence of neonicotinoids in the soil by both studies raises the spectre of a reprise of Rachel Carsons Silent Spring, said Prof Robert Paxton at Martin-Luther-University Halle-Wittenberg in Germany.

The Canadian research also found that the presence of realistic levels of a fungicide made the neonicotinoids twice as toxic to bees. The effect of neonicotinoids on honey bees quickly turns from bad to worse when you add the fungicide boscalid to the mix, said Prof Valrie Fournier, at Laval University in Canada and also part of the team. Pesticides are not tested in combination by regulators and Kerr said: This study shows that mixtures matter.

Environmental campaigners said the new research exposed the full impact of neonicotinoids. The horror story is clear: we have contaminated our land and water with persistent neonicotinoid pesticides, said Matt Shardlow, CEO of the charity Buglife.